If I say: "In the Beginning God created the heaven and the earth."
Everybody says where is your proof? I say it says so in the book of Genesis chapter 1 verse 1. Everybody says the Bible is a lie, it can't be trusted, it is just a myth, it is not a book of science.
Then everybody says where is your proof Goddidit?
A physics textbook is no more proof than a bible. We don't believe in science because it's written in a textbook. We believe it because it can be verified and/or duplicated. We're also not going to tell you that you can't believe in god, but we are going to insist you don't call the existance of god a fact.